This invention relates generally to a sound generator of the type used to electronically produce musical sound and more particularly to a sound generator applying an envelope to musical output signals so as to reproduce the characteristics and the sound of a particular instrument. In the prior art, an envelope has been applied to the output signals for driving a speaker, such as a piezo-electric buzzer, by gradually reducing the duty ratio of the frequency signal applied for driving a speaker. Thereby, the average current flowing through the speaker is gradually reduced to decrease sound pressure and an envelope is applied to the sound signal. A large number of circuit elements are required in the method varying the duty ratio so that ciost of such a product increases substantially. Even in an integrated circuit the increased unit cost for the integrated circuit due to an enlargement of the chip is substantial and is greater that the cost of parts and the cost of assembling the individual parts.
What is needed is a sound generator which applies a desired envelope to the sound signals in a small and economical construction of few electronic components.